The referenced German Patent Disclosure Document DE-OS No. 32 09 821 describes a milling and boring tool element of the type to which the present invention relates. Such a boring tool element has an elongated, essentially cylindrical shank which has spirally extending chip removal grooves. A plurality of pockets are located in the chip removal grooves in which indexable cutter bit inserts are retained. One of these cutter bit inserts is located at the cutting end of the shank radially outwardly. The cutter bit insert has two cutting edges, one extending axially and one extending radially. That cutter bit insert, during boring, removes material from a workpiece by the axially forward cutting edge. During milling, the cutting edge which extends parallel to the axis of rotation, and hence longitudinally of the cutting tool, is effective.
Since in the known boring and milling tool all the cutting edges of one indexable cutter bit insert have the same geometry, a long integral cutter chip is produced on the cutting edge performing the boring operation. Long chips of this kind may occur in the form either a spiral or a ribbon, depending on the material being machined. Both types of chip are extremely troublesome and tend to damage the tool and/or the workpiece.
In the case of the ribbon-shaped chip, a further disadvantage is that it shoots out of the hole being bored at very high speed.
During milling, contrarily, long chips cannot be produced. Their length is intrinsically limited to one-half the circumference of the milling tool. They also have an approximately crescent-shaped form in cross section and so can easily be compressed.